In a case where an image is projected onto a projection surface such as a screen by a projector, it is known that an image formed on the projection surface is distorted in accordance with a projection angle of the projector. A general projector has a trapezoidal distortion correction function for transforming a projected image into a correct shape on the projection surface. When the projector is moved after the trapezoidal distortion correction, the projection angle changes, whereby distortion occurs in the projection image again. Thus, a technique is proposed in which the trapezoidal distortion correction is performed again in a case where a projector having a function of detecting the installation angle detects a change in the installation angle (see, for example, JP-A-2003-283963). The projector disclosed in JP-A-2003-283963 has a function of detecting a tilt angle by using an acceleration sensor and automatically performs trapezoidal distortion correction in a case where the angle of the projector changes by three or more angles.
However, the distortion of the projection image is influenced by not only the tilt angle of the projector but also the projection angle in a horizontal plane. Accordingly, distortion may occur where the relative position of the projector with respect to the projection surface changes. Therefore, in order to respond to the distortion of the projection image that is currently projected, one may detect the movements of the projector in various directions or the movement of the projection surface side. However, according to a general method, it is difficult to detect all the movements.